This invention relates to stabilizers for vinyl ether resist formulations, and more particularly, to stabilizers for vinyl ether based coating compositions that are suitable for imprint lithography.
Imprint lithography has emerged in various forms as a potential alternative to conventional photolithography because of its ability to print smaller features at low cost. UV-cure nanoimprint lithography is a variant of imprint lithography that is amenable to the resolution and overlay requirements necessary for the fabrication of advanced semiconductor devices. In UV-cure nanoimprint lithography, a low-viscosity photosensitive molding material is molded between a mechanically rigid template having a relief pattern and a substrate, and then is exposed to actinic radiation. The resulting hardened layer, having a three dimensional pattern, can for example be used as an etch mask to transfer the imprinted pattern into the substrate below. Other applications are also possible.
Imprint lithography requires low volatility and low viscosity resists to obtain high quality patterned films with uniform composition within the minimum possible cycle time. The composition of the curable material is of critical importance because its components affect the degree of cure, adhesion to the template surface, adhesion to the bottom surface, cohesive strength of the cured material, and the dimensional stability of the imprinted features. Vinyl ether based resists are attractive chemical systems for this purpose because they have low volatility, low viscosity, and also because these materials have very rapid cure rates. Vinyl ether based resist formulations can be cationically cured upon exposure to actinic radiation and the cure chemistry is not affected by free radical traps such as oxygen, thereby reducing the sensitivity of the process to ambient air. Vinyl ether based resists are sensitive to ambient base, however, and their reactions can be inhibited by water vapor.
Prior art cationically curable vinyl ether based imprint resist systems typically contain a vinyl ether crosslinker, a photoacid generator (PAG), an optional reactive vinyl ether diluent, and a stabilizer additive (also commonly referred to a sensitizer additive).
The sensitizer/stabilizer additive, e.g., 9-anthracene methanol, phenothiazine, or coumarin 6, is typically added to inhibit acid induced polymerization reactions caused by degradation of the PAG in the absence of light. Unfortunately, currently available stabilizers such as those noted above are inadequate. For example, the 9-anthracenemethanol stabilizers are insoluble in many vinyl ethers, particularly, silicon-containing vinyl ethers. Also, shelf life is problematic for the 9-anthracenemethanol stabilizers since solidification can occur upon storage at low temperatures. With regard to phenothiazine, a violent reaction with certain kinds of PAG (e.g., 2-[2,2,3,3,4,4,4-heptafluoro-1-(nonafluorobutylsulfonyloxyimino)-butyl]-fluorene) has been observed to occur. Likewise, coumarin 6 has been observed to slow cationic polymerization, which is likely due to the basicity of coumarin 6.
Accordingly, there is a need in the art for improved stabilizers for vinyl ether resists.